Method and apparatus for increasing control response of a vapor generator



R. D. HOTTENSTINE METHOD ANO APPARATUS FOR INCREASING CONTROL Aug. 29, 1967 RESPONSE OF A VAPOR GENERATOR Filed Deo. 29, 1964 0 RICHARD D- HOTTENS'TINE AGEN-r T I WM Nu\\.u\ QQ Nw \w ASI u M m\ E VJ W EN M\ I 8S @L m% mmwv NQQSN@ @S Nwn T Il N\ .\\\Q\\% NN QN NM. KO w IM @SSS wwwww N N k ww im @L IQ I V f www I I Nm MA E# I SQL mw MGIMW I I\%\. i +I II A@ WN H mm n mw@ QN .w .i T IMM N TN E E IISIIIIII lllll I IIII @IEE N N N El NEI N m LISA. mw @il umm, I I lllllllllllllllllll I IW I I IIIII II L EN mm nk United States Patent O 3,338,054 METHOD AND APPARATUS FOR INCREAS- ING CONTROL RESPONSE OF A VAPOR GENERATOR Richard D. Hotteustine, Windsor, Conn., assignor to Combastion Engineering, Inc., Windsor, Conn., a corporation of Delaware Filed Dec. 29, 1964, Ser. No. 421,925 9 Claims. (Cl. 60-107)l This invention relates to vapor generators operating with variable pressure conditions in the superheater and having a throttling valve intermediate the evaporating or water heating section and the superheating section, and in particular the method and apparatus for obtaining the benefit of energy storage in the heating and evaporating portion to aid in transient response of the vapor generator.

It is frequently advantageous at lower than full ratings to operate a steam generator-turbine combination on a variable pressure cycle. Whereas in a conventional cycle the boiler is operated at full pressure at all times with this pressure being throttled by the turbine throttle valve to that required to operate the turbine in the variable pressure system, little or no throttling is done by the turbine throttling valve with the boiler itself operating at reduced pressure. Under such reduced pressure conditions however the changes of speciiic volume which occur in the evaporating section of the boiler may be such as to produce significant stability problems. In order to avoid this a throttling valve is introduced intermediate the evaporating portion and the superheating portion so that the evaporating portion may be operated ata suiiiciently high pressure to avoid stability problems While the superheater is operated at a reduced pressure which is suiiciently high to obtain the desired ow through the steam turbine.

In such a system the inherent heat storage capacity of a conventional steam generator is not available for transient loading conditions. The response therefore is sluggish and in order to obtain an increased steam dow the feedwater ow, fuel and air must be increased before the desired response is obtained. Where the turbine throttle valve is operated in the Wide open position there is no storage in the superheater to permit an intermediate load increase While even if the turbine throttle valve is slightly throttled, the available storage in the superheater is quite limited.

In my inventi'on the throttle valve intermediate the evaporating and superheating portions of the steam generator is opened in response to a sudden increased steam generation demand, thereby taking -advantage of the energy stored Within the evaporating section. Also, this valve is operated in such a manner as to avoid carrying the evaporating portion of the boiler into such a condition that the stability of ow becomes a problem.

It is an object of my invention to provide a vapor generator with improved response characteristics so the transient generation error may be more quickly corrected.

It is a further object to make available to the steam turbine the heat energy stored in the evaporating section of a steam generator in order to improve the response characteristics of the unit.

Other and further objects of the invention will become apparent to those skilled in the art as the description proceeds.

With the aforementioned objects in view, the invention comprises an arrangement, construction and combination of the elements of the inventive organization in such a manner as to attain the results desired, as hereinafter more particularly set forth in the following detailed description of an illustrative embodiment, said embodiment being shown by the accompanying drawing wherein:

The figure is a schematic diagram showing a vapor generator having a throttling valve intermediate the evaporating and superheating portion and employing my invention to operate the throttle valve to make available to the turbine heat storage of the evaporting section.

Feedwater pump 2 supplies feedwater at supercritical pressure through ow nozzle 4 and feedwater valve 6 to the vapor generator. The vapor generator includes a water wall section 8 wherein the water is 'heated to a temperature of about 800 F. Recirculating pump 10 is operative to recirculate Water through the water wall sections with recirculation passing through the recirculating line 12 and the recirculating line check valve 14. Boiler throtttle valve 16 is located downstream of the water wall section and upstream of the divided superheater section including high temperature superheaters 18 and 19. The

steam leaving these superheaters joins in a common turbine steam line 20 with the steam passing through the turbine throttle valve 22 to the steam turbine 24. The steam turbine is connected to an electric generator which is indicated generally on the diagram by output.

Final steam temperature is sensed by steam temperature transmitters 26 and 27 which emit control signals which are compared to the ste-am temperature set points 28 and 29 to determine the temperature error. The temperature error signals of the two superheater sections are compared at summation point 30 with the control signal passing through control line 31 through controller 32 and operating to adjust the feedwater ow, fuel and air to correct the temperature error.

Since this portion of the temperature control system does not have a high rate of response, a tight temperature control loop is also supplied for controlling temperature transients. The temperature error signal from each ste-am temperature transmitter 26 and 27 after being compared to the corresponding set point signals is passed to controllers 34 and 35 from which a signal is emitted through control lines 36 and 37 which are indicative of the desired steam temperature upstream of the superheater section. These signals are compared at summation points 38 and 39 to the control signals 40 and 41 which represent the actual temperature sensed by temperature transmitters 42 and 43. The temperature error signal is passed through control lines 44 and 45 to control injection water valves 46 and 47 injecting spray water through spray Water lines 48 and 49 upstream of the superheaters 18 and 19. The temperature immediately downstream of the boiler throttle valve 16 is sensed by temperature transmitter 97 and a control signal passes to summation point 98 where it is compared to a set point temperature. The temperature error signal is passed through controller 99 to summation point 100. This signal then operates on the eedwater, fuel and air input to bring the temperature to the preselected value. This set point temperature may be programmed to vary with steam generator output.

The input to the steam generator which must 'be controlled includes feedwater iiow, fuel and air. The general input demand signal passes through control line 50 and is divided to pass through control line 51 which is the feedw-ater ow portion and control line 52 which is the heat end portion. This general demand is added at summation points 53 and v54 to similar signals which are passing from the controller 32 and indicate control changes required for steam temperature. The control signal emitting from summation point 53 passes through control line 55 and operates via feedw-ater controller 56 to operate the feedwater control valve in conjunction with the tight control loop illustrated.

The control signal emitting from summation point 54 and indicative of the required heat input of the vapor generator passes through control line 57 and with a signal 4being passed through control line 58 indicative of the required fuel input and a control signal being passed through control line 59 indicative of the required air flow.

to maintain a high 'pressure in the 'water wall section of the vapor generator in order to avoid stability problems. In .a supercritical steam generator a pressure of 3500 'p.s.i. is generally maintained. This pressure can be reduced to the critical pressure of about 3206 without encountering a two-phase measure and therefore any significant sta.- bility problem. In addition, depending on the design of the water wall section a reduction of pressure even below this can in many cases be tolerated. There is however a -definite minimum pressure which should be maintained to avoid instability. Minimum set point setter 64 is set at the Vpreselected minimum pressure, in this case 3200 p.s.i. This signal may pass through the selector 65 and compared at summation point 66 to the control signal passing through control line 67 which represents the actual upstream pressure as sensed by pressure transmitter 68. This operates through controller 69 operating the boiler throttle valve 16 to insure that the upstream pressure at no time during normal operation decreases below the preselected minimum pressure.

Manual set point 70 sends a control signal through control line 71 to the selector with this manual set point being set for the desired normal operating pressure of 3500 p.s.i. The selector 65 will operate in conjunction with this signal sending a control signal to the summation point 66 to control the upstream pressure to the manual set point pressure. The selector however will operate to Iblock the control signal and pass through control line 71 to insure that the pressure never decreases below the minivmum set point position. v

The generation output is sensed by output transmitter 72 with a control signal indicating the actual output passing through control outlet 73. Desired generation set point signal 74 and a -frequency error signal 75 in the event of an alternating current generator are compared at summation point 76 so that a signal representing a desired output passes through control line 77. The desired and actual output signals are compared at summation point 78 with an error signal passing through control line 79 to the controller 80. This signal after proper characterization in the controller passes through control line 81 and summation point 82 operating through control line 83 to activate the governor motor 84. The turbine throttle valve 22 is accordingly operated to vary the steam flow through the turbine and correct the generation error.

'I'he pressure in the superheater is sensed by pressure transmitter `85. A control signal representing `the actual pressure passes through control line l8,8 and -is compared with the pressure set point 89 or desired set point pressure at summation point 90 with Van error signal passing through control line 91 to controller 92. The set point pressure 89 may be characterized with load or operated on any other basis compatible with the desired pressure variable operation of the vapor generator. Control signal representing the pressure error after being characterized by controller 92 passes through the control line 93 to the summation point 82 and then operates to manipulate the turbine throttle valve to maintain the desired upstream pressure.

The generation error passing through control line 81 and the pressure error signal passing through control line 93 are compared at summation point 82 to avoid unnecessary unstability in the control system. If the upstream pressure is higher than desired while the generation is also higher than desired, the turbine throttle valve should not 'be opened because other control actions are operating to reduce the upstream pressure and will, in turn, reduce the generator output.

The characterized signals representing the generation and pressure errors emanating from controllers 80 and 92, respectively, are formed at summation point 94 with -a control signal representing the net error passing through control line 50. This signal operates through control lines 51 and 52 to correct feedwater, fuel and -air inputs to the unit as previously described.

A control signal passes from this control lin-e 50 through control line 95 to summation point 96. This signal represents the net generator output error and operates through the selector 65 in controller 69 to adjust the boiler throttle valve 16. By opening this boiler throttle valve, heat energy stored in the water wall section can be immediately made available to the superheater and thence to the turbine to correct the pressure and generation errors with 4an insignificant time delay. As the feedwater, fuel and air operate to correct the'generation error, the error ceases anda zero error control signal passes through control line 95 so that the control system operates to return the pressure in the Water walls to that established in accordance with the manual set point 70. Due to the significant time delay involved in increasing feedwater flow, yand increasing fuel flow along with the time that it takes to burn this fuel and supply heat not only to the uid contained within the water wall section but also to supply necessary heat for the metal storage, there is considerable time delay in obtaining the benefits of these changes. lThe manipulation of the boiler throttle valve to take advantage of the stored energy in the water wall section significantly reduces the time delay in obtaining corrective actions lat the turbine and generator. The minimum set point signal 64 is still in operation operating through selector 65 and should the generation error attempt to drive the desired upstream pressure below the safe minimum set by this minimum set point 64, the selector 65 will block out the signal passing through control line 71 so that the minimum safe upstream pressure is maintained.

The steam generated illustrated is of the recirculation type. Fluid leaving the water wall section 8 is recirculated Vthrough recirculating line 12 to the inlet of the Water wall section. This operates to increase the temperature of the uid entering the Water wall section, thereby increasing the temperature level throughout the section. Such a unit 'has considerable heat storage in the water wall section which is made available for transient response by my invention.

The control system of my invention may be either electrical in nature, hydraulic, or may employ air pressure. An electric system is preferred because of its convenience, and the controllers indicated may be either controllers of the type manufactured by Leeds and Northrup Company, the Hagan Company, or others which manufacture integrating type controllers. These controllers will supply proportional action in which case the signal emitted is in some manner proportional to the signal received and they can also provide integrated signals wherein the emitted signal increases in strength in some proportion with the time during which the received signal has varied from the desired value. The temperature pressure and flow transmitters may be of the standard Leeds and Northrup Company or Hagan Company type with these transmitters transmitting a signal that is compatible with the controller inputs.

While I have illustrated and described the preferred embodiment of my invention, it is to -be understood that such is merely illustrative and not restrictive and that variations and modifications may be made therein without departing from the spirit and scope of the invention. I therefore do not wish to be limited to the precise details set forth but desire to avail myself of such changes as fall within the purview of my invention.

What I claim is: 1. A method of operating a vapor generator comprising: passing flui'd at a preselected high pressure through conduits and imparting heat to the fiuid; throttling the flow of the fluid to reduce the pressure thereof; regulating the amount of throttling to control said preselected pressure of the fluid; passing the iluid egressing from the throttling means through conduits at a lower pressure and imparting additional heat to the iluid; conveying the low pressure fluid through a steam turbine generating a power output; sensing the output of the steam turbine; comparing the sensed output to a desired output and obtaining an output error signal; sensing the pressure of the fluid at reduced pressure; comparing the sensed pressure to a desired pressure and obtaining a pressure error signal; combining the pressure error signal with the output error signal, obtaining a net error signal; regulating the heat input and iluid ilow in response to the net error signal in a direction to correct the error; simultaneously varying the throttling of the iluid in response to the error signal in the direction to correct the net error.

2. A method of operating a vapor generator cornprising: establishing a llow of fluid at a preselected high pressure; transferring heat to said fluid at high pressure; throttling the iluid to a lower pressure; regulating the throttling of the tluid to maintain said preselected pressure; transferring heat to the fluid at reduced pressure; thereafter conveying the tluid to a stream turbine generating a power output; sensing the output of the steam turbine; establishing a desired output; comparing the desired output with the measuring output and obtaining therefrom an output error; varying in response to the error the feedwater llow and heat input to the fluid in a direction to satisfy the error; simultaneously in response to the error signal varying the throttling of the fluid in a direction to satisfy the error.

3. A method of operating a vapor generator com-prising: establishing a ilow of lluid at a preselected high pressure; transferring heat to said lluid at high pressure; throttling the iluid to a reduced pressure; regulating the throttling of the uid to maintain said preselected high pressure at an upstream location; transferring heat to the fluid at said reduced pressure; thereafter conveying the4 tluid to a steam turbine generating a power output; sensing the pressure of the iluid at said reduced pressure; establishing a desired reduced pressure; comparing the desired reduced pressure with the sensed reduced pressure and obtaining therefrom a pressure error; varying in response to the pressure error the feedwater ow and heat input to the fluid in a direction to satisfy the error; simultaneously t in response to the pressure error varying the throttling of the fluid in a direction to satisfy the error, while temporarily disregarding said preselected high pressure at an upstream location.

4. A method of operating a vapor generator comprising: passing iluid through a supercritical pressure portion of the vapor generator and imparting heat to the tluid; throttling the llow of lluid establishing a subcritical portion of the Vapor generator downstream of the throttling location; regulating the throttling of the fluid to maintain a preselected pressure in the supercritical pressure portion of the vapor generator; imparting heat to the iluid in the subcritical portion of the vapor generator; conveying the fluid at subcritical pressure to a steam turbine, generating a power output, and sensing the output of said steam turbine; establishing a desired output and comparing the desired output to the actual output determining an output error; varying the fluid flow and heat input to the lluid in response to the output error in a direction to satisfy the error; simultaneously in response to 4the output error varying the preselected pressure of the supercritical portion of the vapor generator, so that the throttling means in acting to maintain this new selected pressure varies the output of the turbine in the direction to satisfy the error.

5. A method of operating a vapor generator comprising: passing iluid through a supercritical pressure portion of the vapor generator and imparting heat to the uid; throttling the llow of iluid establishing a subcritical portion of the vapor generator downstream of the throttling location; regulating the throttling of the fluid to maintain a preselected pressure in the supercritical pressure portion of the vapor generator; imparting heat to the iluid in the subcritical portion of the vapor generator; conveying the iluid at subcritical pressure to a steam turbine, generating a power output, and sensing the output of said steam turbine; establishing a desired output and comparing the desired output to the actual output determining an output error; sensing the pressure of the uid in said subcritical portion of the Vapor generator; establishing a desired pressure in said subcritical portion of the. vapor generator; comparing the desired pressure with the sensed pressure obtaining a pressure error; summing the output error and pressure error obtaining a net error; varying the fluid low and heat input to the lluid in response to the net error in a direction -to satisfy the error; simultaneously in response to vthe net error varying the preselected pressure of the supercritical portion of the vapor generator, so that the throttling means in acting to maintain this new selected pressure varies the pressure in the subcritical pressure portion of the vapor generator and the output of the turbine in the direction to satisfy the net error.

6. A method as in claim 4 including: establishing a preselected minimum acceptable pressure for the supercritical portion of the vapor generator; and limiting the variations in the preselected pressure rof the supercritical portion 0f the vapor generator so that it remains at all times above the preselected minimum acceptable pressure.

7. A vapor generator for variable pressure operation comprising: a supercritical pressure fluid heating portion and a subcritical tluid heating portion; throttling means located intermediate said subcritical and supercritical portions; means for regulating the fluid flow through said vapor generator and means for regulating heat input to said vapor generator; means conveying the elluent of the vapor generator to a steam turbine; means sensing the output of the steam turbine; means for comparing a desired output with the sensed output and establishing an output error signal; means for sensing the pressure in said subcritical fluid heating portion; means for comparing a desired pressure in said subcritical portion with the sensed pressure and establishing a pressure error signal; means for summing the output error signal and pressure error signal for obtaining a net error signal; means for regulating the lluid ilow and heat input in response to said net error signal in a direction to correct the error; and means for simultaneously varying the throttling means in response to the error signal in a direction to correct the error.

8. A vapor generator for variable pressure operation comprising: a supercritical pressure fluid heating portion and a subcritical lluid heating portion; throttling means located intermediate said subcritical and supercritical portions; means for regulating the lluid ilow through said vapor generator and means for regulating heat input to said vapor generator; means conveying the ellluent of the vapor generator to a steam turbine; means sensing the output of the steam turbine; means for comparing the desired output with the sensed output and establishing an output error signal; means for regulating the lluid ilow and heat input in response to said error signal in a direction to correct the error; and means for simultaneously varying the throttling means in response to the error signal in a direction to correct the error.

9. A vapor generator for variable pressure operation comprising: a supercritical pressure lluid heating portion and a subcritical tluid heating portion; means for recirculating the fluid through at least a portion of said supercritical portion so that the fluid within the supercritical portion will be maintained at a generally high level; throttling means located intermediate said subcritical and supercritical portions; means for regulating the iluid ilow through said vapor generator and means for regulating heat input to said vapor generator; means conveying the etlluent of the vapor generator to a steam turbine; means sensing the output of the steam turbine; means for comparing a desired output with the sensed output and establishing an output error signal; means for sensing the pressure in said subcritical uid heating portion; means for comparing a desired pressure in said subcritical portion with the sensed pressure and establishing a pressure error signal; means for summing the output error signal and pressure error signal for obtaining a net error signal; means for regulating the fluid flow and heat input in response to said net error signal in a direction to correct the error; and means for simultaneously varying the throttling means in response to the error signal in a direction to correct the error.

ReferencesrCted UNITED STATES PATENTS Iunkins 60-107 X Eglo 60-107 Donaldson 60-105 X Bristol 60-105 X *Buri 60-105 Hickox 60-105 X Daniels 60--107 X MARTIN P. SCHWADRON, Primary Examiner.

ROBERT R. BUNEVICH, Examiner. 

1. A METHOD OF OPERATING A VAPOR GENERATOR COMPRISING: PASSING FLUID AT A PRESELECTED HIGH PRESSURE THROUGH CONDUITS AND IMPARTING HEAT TO THE FLUID; THROTTLING THE FLOW OF THE FLUID TO REDUCE THE PRESSURE THEREOF; REGULATING THE AMOUNT OF THROTTLING TO CONTROL SAID PRESELECTED PRESSURE OF THE FLUID; PASSING THE FLUID EGRESSING FROM THE THROTTLING MEANS THROUGH CONDUITS AT A LOWER PRESSURE AND IMPARTING ADDITIONAL HEAT TO THE FLUID; CONVEYING THE LOW PRESSURE FLUID THROUGH A STEAM TURBINE GENERATING A POWER OUTPUT; SENSING THE OUTPUT OF THE STEAM TURBINE; COMPARING THE SENSED OUTPUT TO A DESIRED OUTPUT AND OBTAINING AN OUTPUT ERROR SIGNAL; SENSING THE PRESSURE OF THE FLUID AT REDUCED PRESSURE; COMPARING THE SENSED PRESSURE TO A DESIRED PRESSURE AND OBTAINING A PRESSURE ERROR SIGNAL; COMBINING THE PRESSURE ERROR SIGNAL WITH THE OUTPUT ERROR SIGNAL, OBTAINING A NET ERROR SIGNAL; REGULATING THE HEAT INPUT AND FLUID FLOW IN RESPONSE TO THE NEXT ERROR SIGNAL IN A DIRECTION TO CORRECT THE ERROR; SIMULTANEOUSLY VARYING THE THROTTLING OF THE FLUID IN RESPONSE TO THE ERROR SIGNAL IN THE DIRECTION TO CORRECT THE NEXT ERROR. 